In typeck, check for dynamically sized by-value arguments to thunks

A check in trans didn't have a corresponding check in typeck, causing
some programs (to wit, compile-fail/chan-parameterized-args.rs - part of this
commit) to fail with an assertion failure in trans instead of a type error.
Fixed it. In short, arguments that are future thunk arguments (any spawn
arguments, and _ arguments in bind) need to either not contain type params
or type vars, or be by-reference.

Closes #665.

src/test/compile-fail/bind-parameterized-args.rs

@@ -0,0 +1,10 @@
+// xfail-stage0
+// error-pattern:Bind arguments with types containing parameters must be
+fn main() {
+  fn echo[T](int c, vec[T] x) {
+  }
+  
+  let fn(vec[int]) -> () y = bind echo(42, _);
+
+  y([1]);
+}

src/test/compile-fail/chan-parameterized-args.rs

@@ -0,0 +1,18 @@
+// xfail-stage0
+// error-pattern:Spawn arguments with types containing parameters must be
+fn main() {
+// Similar to bind-parameterized-args
+    fn echo[T](chan[T] c, chan[chan[T]] oc) {
+        let port[T] p = port();
+        oc <| chan(p);
+
+        auto x;
+        p |> x;
+        c <| x;
+    }
+
+    auto p = port[int]();
+    auto p2 = port[chan[int]]();
+
+    spawn echo(chan(p), chan(p2));
+}